Perforation tool having dissolvable plugs and methods of using same

ABSTRACT

Described herein is a perforation tool having dissolvable plugs and methods of using same. The tool may have a tubular housing having holes where each hole extends through the wall, and dissolvable plugs placed in the holes. The dissolvable plugs may be made of dissolvable material that extends from an interior face of the tool to an exterior face of the tool. The tool may be placed in a well proximal to the formation, the dissolvable plugs may be dissolved, and fluid may be provided to the formation. More than one tool may be used to sequence fracturing of respective formations. After a first formation is fractured a diverter may be used to divert fluid away from holes communicating to the fractured formation so that fracturing of the second formation may be selectively performed.

RELATED APPLICATIONS

This application claims priority to U.S. application No. 62/925,050 filed on Oct. 23, 2019 which is hereby incorporated by reference.

FIELD

The invention generally relates to Oil and Gas (O&G) wells, and in particular to a perforation tool having dissolvable plugs and methods of using same. The tools are particularly suited for use in well stimulation operations or for controlling production from different production zones.

BACKGROUND

Hydrocarbons, such as O&G, may be recovered from various types of subsurface geological formations. The formations typically consist of a porous layer, such as limestone and sands, overlaid by a nonporous layer. Hydrocarbons cannot rise through the nonporous layer, and thus, the porous layer forms a reservoir in which hydrocarbons are able to collect.

In a simplified drilling and completion process, a well is drilled through the earth until the hydrocarbon bearing formation is reached. After drilling, steel casing is positioned in the well and at least partially cemented in place to prevent the sides of the borehole from caving in and to reduce the risk of fluid communication between the well and groundwater reservoirs. The casing is then perforated at or near a production zone (i.e. a formation or portion thereof targeted for O&G production) to allow O&G to flow from the formation into the well. Well stimulation techniques, such as mechanical or hydraulic fracturing (hereinafter, collectively “fracturing”), may be used to improve O&G production rates by improving fluid communication within the formation.

Fracturing techniques have undergone continual development since their creation over half a century ago. Common methods of fracturing include “plug and perf” or using fracturing valves, both of which can be time consuming and costly and require additional equipment to be positioned downhole apart from production casing.

Dissolvable materials have found certain applications in O&G completion and production, at least in part due to their ability to allow certain procedures to be performed without sustained interaction from the well-head. That is to say, dissolvable materials may be placed downhole and do not need to be recovered or manipulated before production can continue or resume.

For example, U.S. Pat. No. 7,527,103 describes methods and compositions for protecting a reservoir from damage during drilling-in, completion and production. In one embodiment, a cylindrical casing liner has a pseudo-filter cake deposited by drill-in fluid. The pseudo-filter cake prevents or inhibits the flow of liquids and must be removed prior to the flow of hydrocarbons from subterranean formation commencing. Such methods depend on adequate deposition of a pseudo-filter cake from the drill-in fluid, the thickness and composition of which could vary based on drilling parameters.

There remains a need for new and effective uses for dissolvable technologies during well completion and production.

SUMMARY

According to one aspect, there is provided a perforation tool for use in a production well, the perforation tool having a tubular housing having a wall defining a channel, the housing comprising one or more holes, each hole extending through the wall; and one or more dissolvable plugs, each dissolvable plug connected to the housing in order to seal the respective hole, wherein each dissolvable plug comprises dissolvable material that extends from an interior face of the housing to an exterior face of the housing such that when the dissolvable material is dissolved, fluid communication through the wall is enabled via the holes.

The tubular housing may be of unitary construction. Each dissolvable plug may be of unitary construction. The tubular housing may form part of the production casing.

When in place, the inner and outer surfaces of the plug may lie flush with the inner and outer surfaces of the wall. That is, the plug may span the depth of the hole such that, when it is in place, the plug forms substantially smooth surface with the inner and outer surfaces of the wall. This may help the casing to be installed, and tools to move within the casing.

The axial dimension of the plug may be greater than the diameter of the plug. The diameter of the hole may be less then the thickness of the wall. That is, the plug may be longer than it is wide. This may allow the plug to better resist the pressure exerted between the inside of the channel and the outside. This may be particularly important in fracturing operations where one or more of the plugs have been selectively dissolved, and one or more of the plugs remain intact. It is important that the undissolved plugs can resist the pressure while hydraulic fracturing operations are taking place through the holes vacated by the selectively dissolved plugs. Narrower and longer holes may also allow the pressure of the flow of the hydraulic fluid to be directed. That is, the hole may act as a nozzle for focusing the flow onto a particular portion of the formation.

Each dissolvable plug and respective hole may be connected by complementary screw threads.

The dissolvable material may include magnesium.

The housing may include about ten holes.

Each hole may have a cross section at the interior face of the housing of about 0.38 inches.

The holes may be arranged in a longitudinal spiral or helix about the housing, each hole being radially disposed about 60° from a neighboring hole in the longitudinal spiral. Each hole being radially disposed between 30-120° from a neighboring hole in the longitudinal spiral. The helix angle of the spiral of holes may be greater than 45°. A helix angle is the angle between the helix and the axis of the tubular housing.

The housing may further include: a first section with a box thread to connect the housing to a first section of production casing; and a second section with a pin thread to connect the housing to a second section of production casing.

According to a further aspect, there is provided a method for fracturing a production zone, the method including the steps of: providing a perforation tool described herein in a well proximal to the production zone; dissolving one or more of the one or more dissolvable plugs; and providing fluid to the production zone through holes with a dissolved plug to fracture the production zone.

The dissolving step may be performed at between about 2,000 and about 10,000 psi.

The dissolving step may be substantially completed within 2-10 days. The dissolving step may be substantially completed within about 7 days. The dissolving step may be substantially completed within about 3 days. The duration of the dissolving step may be predetermined or controlled based on a combination of one or more of: the size and shape of the plugs (e.g. plugs with a larger amount of dissolvable material will take longer to dissolve); the material composition of the plug; and/or the fluid in contact with the dissolvable plug. The perforation tool may comprise a series of plugs configured to have different dissolving rates. The perforation tool may be configured such that plugs nearer the wellhead have a slower dissolving rate.

The dissolving step may be performed at between about 10 wt % about 25 wt % chlorides.

The dissolving step may be performed at between about 0 wt % and about 10 wt % chlorides.

The dissolving step may include providing an acid to the dissolvable plugs.

The method may further include the steps of: providing a second perforation tool described herein in the well proximal to a second production zone; dissolving one or more of the one or more dissolvable plugs of the second perforation tool; and providing fluid to the second production zone through holes of the second perforation tool with a dissolved plug to fracture the second production zone.

The method may comprise providing a diverter to the first perforation tool to prevent fluid flow to the first production zone.

The providing the diverter step may be performed simultaneously with the providing fluid to the first production zone.

The dissolvable plugs of the second perforation tool may be configured to dissolve at a slower rate than the dissolvable plugs of the first perforation tool.

The first production zone and the second production zone may belong to a same formation.

The step of dissolving one or more of the plurality of dissolvable plugs of the first perforation tool may include providing a first dissolving fluid to the first perforation tool, and the step of dissolving one or more of the plurality of dissolvable plugs of the second perforation tool comprises providing a second dissolving fluid to the second perforation tool.

The apparatus and method may be used in conjunction with hydraulic fracturing operations.

According to a further aspect, there is provided a hydraulic fracturing system comprising: a perforation tool as described above; and a pump configured to pump fluid into the perforation tool. The perforation tool may form part of a casing (e.g. the formation casing). The perforation tool may be configured to be in direct contact with the rock formation.

Hydraulic-fracturing equipment used in oil and natural gas fields usually comprise one or more high-pressure, high-volume fracturing pumps and a monitoring unit. Associated equipment may also include one or more fracturing tanks, one or more units for storage and handling of proppant, a chemical additive unit (used to accurately monitor chemical addition), low-pressure flexible hoses, and/or gauges and meters for flow rate, fluid density, and treating pressure. Chemical additives are typically 0.5% or less of the total fluid volume. Fracturing equipment may operate over a range of pressures (up to 15,000 psi) and injection rates (up to 265 liters per second). The pumps may be configured to apply a pressure of more than 2,000 psi to the fluid. The pumps may be configured to apply a pressure of up to than 10,000 psi to the fluid. The pumps may be configured to apply a pressure of up to than 15,000 psi to the fluid. The pump may be located at the surface.

Fracturing fluid may comprise a slurry of water and proppant. Typically, most of the fluid is water (e.g. 75-95% volume) and sand or other proppant (e.g. 5-25%), optionally with chemical additives generally accounting less than 1% volume.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings. Similar reference numerals indicate similar components:

FIG. 1 is a perspective view of a tubular housing tool, according to one embodiment;

FIG. 2 is a longitudinal cross section of the tubular housing along line 2-2 of FIG. 1;

FIG. 3 is an elevation view of the tubular housing shown in FIG. 1;

FIG. 4 is a detailed view of a hole of the tubular housing shown as “B” in FIG. 2;

FIG. 5 is a transverse cross section of the perforation tool along line 5-5 of FIG. 1;

FIG. 6 is a perspective view of a dissolvable plug, according to one embodiment;

FIG. 7 is a longitudinal cross section of the dissolvable plug along line 7-7 of FIG. 6;

FIG. 8 is a flow chart of a method for fracturing a production zone using the tool described herein;

FIG. 9 is a schematic view of two perforation tools deployed in a well; and

FIG. 10 is a detailed view of a further embodiment of a hole with a dissolvable plug positioned therein.

DETAILED DESCRIPTION Introduction and Rationale

The present inventors, having a background in design and manufacture of tools for the extraction of O&G, observed that certain aspects of completion and production could be improved by the application of dissolvable materials. Specifically, the inventors noticed that there was a need to reduce the cost in completion and production operations by reducing the number of interventions required at the well head.

It is desirable to reduce the number of interventions for a number of reasons, including: there is less time is required to perform completion steps; there is less reliance of techniques that manipulate downhole equipment, such as coiled tubing; and there may be improved safety at the well-head.

Therefore, embodiments of the present invention may avoid certain drawbacks associated with known completion and production techniques. In addition, the tools described herein may be simple and cost-effective to manufacture and deploy in O&G operations.

EQUIVALENTS AND SCOPE

Other than described herein, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages, such as those for amounts of materials, elemental contents, times and temperatures, ratios of amounts, and others, in the following portion of the specification and attached claims may be read as if prefaced by the word “about” even though the term “about” may not expressly appear with the value, amount, or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

While this invention has been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

In the claims, articles such as “a,” “an,” and “the” may mean one or more than one unless indicated to the contrary or otherwise evident from the context. Claims or descriptions that include “or” between one or more members of a group are considered satisfied if one, more than one, or all of the group members are present in, employed in, or otherwise relevant to a given product or process unless indicated to the contrary or otherwise evident from the context. It is also noted that the term “comprising” is intended to be open and permits but does not require the inclusion of additional elements or steps.

Structure and Operation of a First Embodiment

A first embodiment of the perforation tool will be described with respect to FIGS. 1-7 and 10.

FIG. 1 shows a tubular housing 100 having a wall 102 a defining a channel 102 b. A longitudinal axis 100 a is shown extending through the center of the tubular housing 100. The tubular housing 100 has a first end 104 and a second end 106 and ten holes extending through the wall 102 a. In this case, the first and second ends 104, 106 are open to allow fluid to pass through the channel 102 b. While there are ten holes shown in FIG. 1, only three holes 108 a,108 b,108 c are labelled for clarity of the drawings. The tubular housing 100 has an exterior face 110 and an interior face 112, with the holes extending continuously from the exterior face to the interior face thereby permitting fluid communication between the channel 102 b and an exterior of the housing when the holes are not blocked. In an embodiment the tubular housing 100 may be about 22 inches long and between about 1.0 and about 1.5 inches thick at the first end 104.

As will be further described in relation to FIG. 9 below, the first end 104 may have a box thread on the interior face 112 to connect to a first portion of production casing, and the second end 106 may have a pin thread on the exterior face 110 to connect to a second portion of production casing. Inclined shoulder 106 a at the second end 106 may receive an end of the second portion of production casing once threaded onto the tubular housing 100. Other means to connect the tubular housing 100 to neighboring production casing are also contemplated. For example, compression fittings may couple the production casing and the tubular housing 100, or recesses in the tubular housing may mate with projections on the production casing, or vice versa.

The holes extending through the wall 102 a are arranged in a longitudinal spiral about the tubular housing 100. In the embodiment shown in FIGS. 3 and 5, the holes are radially disposed about the tubular housing 100 about 60° from a neighboring hole, and a centerline of each of the holes is between about 1″ and about 1.1″ along the axis 100 a from a centerline of a neighboring hole. The radial displacement may be seen most clearly in FIG. 5, which shows that, when viewed along the axis 100 a, hole 108 a is radially disposed about 60° from hole 108 b and radially disposed about 180° from hole 108 d. In this embodiment, “neighboring” is understood as referring to the next hole (e.g. the closest hole) in the longitudinal spiral about the housing 100.

Other hole configurations and total number of holes are also contemplated. For instance, the radial degrees between neighboring holes and the longitudinal displacement of the neighboring holes about the axis 100 a are only exemplary. For example, a spiral having more turns about the axis 100 a per displacement along the axis may be achieved by increasing the degrees of separation between neighboring holes. Configurations may also include non-symmetrical distributions and/or clusters of holes in particular areas along the housing 100. In certain embodiments, the housing may have as few as one hole. In other embodiments, the housing may have three holes radially disposed about 120° from each other hole on a plane substantially orthogonal to the axis 100 a. The specific configuration and total number of holes will depend at least on the desired fracture and/or production dynamics from the production zone.

FIG. 4 is a detailed view of the hole 108 a of the tubular housing 100. In the particular embodiment shown in FIG. 4, the hole has shoulders 402 b,402 c. The shoulders 402 b,402 c, in combination with the exterior face 110 and the interior face 112, bound faces 404 a,404 b,404 c of the hole. The face 404 a has threads 408 extending towards axis 406.

The faces 404 a,404 b,404 c may be about 0.37″, 0.19″ and 0.12″ long, respectively. The diameter of the faces 404 a,404 b,404 c relative to the axis 406 may be about ⅝″, 0.50″ and 0.38″, respectively. Therefore, the hole 108 a has a cross section at the interior face 112 of about 0.38″.

The holes are adapted to be connected to dissolvable plugs having dissolvable material that extends from the interior face 112 to the exterior face 110 such that when the dissolvable material is dissolved, fluid communication through the wall 102 a is enabled via the holes.

FIGS. 6 and 7 show an exemplary dissolvable plug 600 having an axis 608 extending therethrough. Referring to both FIGS. 6 and 7 together, dissolvable plug 600 has faces 604 a,604 b, with shoulders 602 c,602 d bounding the face 604 b. The face 604 a has threads 610 extending away from axis 608.

The faces 604 a,604 b may be about 0.3″ and 0.09″ long, respectively. The diameter of the faces 604 a,604 b about the axis 608 may be about 0.56″ and 0.40″, respectively.

When the dissolvable plug 600 is installed in the hole 108 a, for example, the axis 608 is coaxial with the axis 406. To install the plug 600 in the hole 108 a, the plug may be turned by the slot 606 so that the threads 610 engage with the threads 408. The plug 600 may be advanced until the threads 610 abut the shoulder 402 b, thereby preventing further lateral displacement of the plug towards the channel 102 b. The shoulders allow the plug to be tightly engaged with the hole.

The shoulders 602 c,602 d define a space to receive an o-ring for sealing engagement between the face 604 b of the dissolvable plug 600 and the face 404 b of the hole 108 a. In one embodiment, the O-ring may have about a 0.40″ interior diameter. Although not necessary, a sealed connection between the dissolvable plug 600 and the hole 202 a may be desirable to prevent fluid communication between the well and the formation before the dissolvable plug has dissolved.

The dissolvable plug 600 may comprise any dissolvable material that may selectively dissolve when exposed to fluids present in the well or in the production zone. For example, magnesium alloys are known to be sufficiently strong when dry, but dissolve readily when exposed to select well fluids. Other dissolvable materials may include Copper or nickel alloys, including certain additives that may delay or accelerate dissolution of the plug.

In the embodiment shown in FIGS. 6 and 7 the dissolvable plug 600 is made entirely of dissolvable material; however, in other embodiments only a portion of the dissolvable plug may be made from dissolvable material provided that, once the dissolvable material is dissolved, fluid communication through the dissolved portion of the plug is enabled. For example, the plug may comprise a dissolvable plug channel through the plug or the plug may be configured to fall out of the hole when the dissolvable material is dissolved.

It is contemplated that one dissolvable plug 600 may be placed in each of the holes on the housing 100 to seal the respective hole, thereby restricting fluid flow to the channel 102 b until such time that one of the dissolvable plugs substantially dissolves. For a fixed tubular housing, the arrangement of dissolvable holes may also be controlled by selectively inserting dissolvable plugs in some of the holes, and non-dissolvable plugs in others.

Other types of plugs and holes are contemplated. For example, FIG. 10 is a detailed view of a further embodiment of a hole with a dissolvable plug positioned therein. FIG. 10 shows a hole 1000 a and a plug 1000 b. The hole 1000 a has shoulders 1002 a,1002 b,1002 c. The plug 1000 b has a projection 1004 and two O-rings 1006 a,1006 b disposed radially thereon.

In the embodiment shown in FIG. 10 the plug 1000 b is retained in the hole 1000 a by engagement between the projection 1004 and the shoulders 1002 a,1002 c. An advantage of using two O-rings includes that a portion of the plug 1000 b may be isolated from fluids from both the well and formation, thereby providing better sealing between the well and formation.

To insert the plug 1000 b into the hole 1000 a, the plug may simply be advanced until the projection 1004 snaps into the space between the shoulders 1002 a,1002 c. It will be appreciated that a certain amount of elastic deformation by the projection 1004 or the hole 1000 a may be required for the projection to advance past the shoulder 1002 b.

Methods Using the Perforation Tool

Having described an example perforation tools with reference to FIGS. 1 to 7, methods of using the perforation tools described herein will now be discussed.

With reference to FIG. 8, a method 800 of fracturing a production zone may include: at step 802, providing a perforation tool described herein in a well proximal to a production zone; at step 804, dissolving one or more of the dissolvable plugs; and at step 806, providing fluid to the production zone through holes with a dissolved plug to fracture the production zone. While the perforation tool may be the perforation tool 100 described herein, other perforation tools may work equally well with the method 800.

Providing a Perforation Tool

In step 802 the perforation tool may be provided by threadedly connecting the first end of the perforation tool to a first section of production casing and by threadedly connecting the second end of the perforation tool to a second section of production casing, for example, while the production casing is being positioned or lowered into the well.

As used in the present specification, “proximal” means sufficiently close to the production zone such that fluid communication is possible between the production zone and the perforation tool. Therefore, to be proximal to a production zone the perforation tool need not necessarily be in the production zone.

Dissolving One or More Dissolvable Plugs

The step of dissolving one or more of the dissolvable plugs may begin automatically by placing the perforation tool downhole or may be commenced by manipulating fluid parameters at the perforation tool, such as a specific fluid being pumped downhole to commence the dissolution of the dissolvable plugs.

For example, an increase in pressure in the well may accelerate the dissolution of the dissolvable plugs. In an embodiment, the dissolvable plugs may be dissolved at a pressure between about 0 to about 10,000 psi. In a preferred embodiment, the dissolvable plugs may be dissolved at a pressure between about 2,000 to about 10,000 psi.

In another embodiment, the wt % chloride in the well fluids or formation fluids may determine the rate of dissolution of the plugs. For example, dissolving the dissolvable plugs may occur when between about 10 wt % and about 25 wt % chlorides are present. In another embodiment, dissolving the dissolvable plugs may occur when between about 0 wt % and about 10 wt % chlorides are present.

Certain dissolution times may be particularly preferred. For example, in one embodiment the dissolving step may be substantially completed within about 1 month. In another embodiment, the dissolving step may be substantially completed within about 7 days. In another embodiment, the dissolving step may be substantially completed within about 3 days.

In embodiments where fluid is pumped downhole to at least in part dissolve the dissolvable plugs, the dissolving step may include providing an acid to the dissolvable plugs. In one embodiment, the acid may be between about 5 wt % HCl and about 28 wt % HCl. In a particularly preferred embodiment, the acid may be about 7 wt % HCl.

In the present specification, the term dissolving shall mean that the dissolvable plug has dissolved or degraded to such a degree that fluid may be communicated between the channel and an exterior of the housing. Therefore, complete dissolution or degradation is not necessarily required for the dissolvable plug to be said to have “dissolved”. Notably, not all dissolvable plugs need to be dissolved to provide fluid communication from the channel to the exterior of the housing. In certain embodiments, it may be sufficient for as few as one dissolvable plug to dissolve to permit completion and or production from the production zone.

It will be appreciated that dissolving the plug may reduce the strain applied to the casing compared with other perforation methods, such as using a perforating gun. Therefore, this method may help ensure the integrity of the casing.

Providing Fluid to the Production Zone

Step 806 may include pumping fluid from the wellhead to the perforation tool to increase the pressure at the production zone. As one or more of the dissolvable plugs have dissolved, fluid will flow from the channel to the exterior of the housing thereby increasing the pressure observed at the production zone and fracturing the production zone.

While fracturing is particularly contemplated, other well stimulation techniques, such as acidizing the production zone after dissolving one or more of the dissolvable plugs could also or additionally be used.

Further Method Steps

Methods are contemplated where more than one perforation tool is used. For example, in addition to the method steps 802,804,806, an exemplary method may also include the steps of: providing a second perforation tool in the well proximal to a second production zone; dissolving one or more of the dissolvable plugs of the second perforation tool; and providing fluid to the second production zone through holes of the second perforation tool with a dissolved plug to fracture the second production zone. In an embodiment, although not required, the second perforation tool may be the housing 100 with the dissolvable plugs 600.

Where two or more perforation tools are used, the exemplary method may further include the step of providing a diverter to the first perforation tool to prevent fluid flow to the first production zone. In this way, the diverter may be used to selectively seal the well from the first production zone. This may be advantageous so that specific fracturing mechanics may be achieved at the second production zone without concern that fracturing the second production zone may affect the fracturing profile at the first production zone. The second production zone may be closer to the wellhead than the first production zone.

A diverter is a separate tool or component that prevents well fluid from contacting fluid in a production zone at a specific perforation tool. A diverter could be a ball that travels with fluid down the well towards the first perforation tool to seal against an annular projection in the first perforation tool. The annular projection may be formed in the tubular housing. In this embodiment, the ball may be placed in the fluid being pumped downhole at step 806, for example, so that after a specific length of time fluid communication between the well and the first production zone may stop and fracturing of the second production zone may begin. In this embodiment, the providing the diverter step would be performed simultaneously with the providing fluid to the first production zone step. This embodiment may have the advantage of substantially reduced downtime, as fracturing of the second production zone may begin shortly after fracturing of the first production zone has terminated.

Other diverters are contemplated and may work equally well. For example, known diverters may have specific flow channels that allow fluid being pumped downhole to bypass the holes of the target perforation tool. Specific diverters could include a tube designed to rest within the channel of the perforation tool or materials designed to temporarily or permanently plug the holes of the perforation tool, such as glass beads or crystals, for example.

Certain completion and production methods that may be achieved using the perforation tools described herein with or without a diverter may be considered with respect to the schematic shown in FIG. 9.

FIG. 9 is a schematic of a well with two perforation tools after the dissolvable plugs have dissolved. In FIG. 9, the well 900 is bounded by production casing sections 902,906,910. Production casing sections 906,910 are connected to a first perforation tool 908 and production casing sections 902,906 are connected to a second perforation tool 904. The well 900 traverses production zone 912,914,916, with perforation tool 908 in production zone 916 and perforation tool 904 in production zone 912. It will be appreciated that production zones 912,914,916 may be in the same formation or in different formations, and fluid communication may be possible between production zones 912,914 or production zones 914,916. As shown in FIG. 9, the perforation tool, in this case, is configured to be in direct contact with the rock formation. This means that when the plugs are dissolved, pressurized frac fluid can be directly injected into the rock.

Using more than one perforation tool permits tailoring completion and/or production with increased accuracy. For example, in one embodiment the dissolvable plugs of the second perforation tool 904 may dissolve at a slower rate than the dissolvable plugs of the first perforation tool 908. This will mean that when, for example, fluid is pumped down the well 900 to fracture the production zone 916, fluid communication to the production zone 912 would have been prevented as the dissolvable plugs of perforation tool 904 had not yet dissolved. Optionally, a diverter may temporarily or permanently seal the holes of the second perforation tool 908 after the production zone 916 has been fractured to permit selective fracturing of the production zone 912.

In a further embodiment, different fluid may be used to dissolve the plugs of each perforation tool. For example, the step of dissolving one or more of the plurality of dissolvable plugs of the first perforation tool may include providing a first dissolving fluid to the first perforation tool and the step of dissolving one or more of the plurality of dissolvable plugs of the second perforation tool may include providing a second dissolving fluid to the second perforation tool. An exemplary embodiment may include where fluid with a lower chloride wt % may effect the dissolution of the plugs of the first perforation tool, but fluid with a higher chloride wt % is required to dissolve the plugs of the second perforation tool within a given timeframe. In this embodiment, as fluid is pumped from the wellhead into the formation 916, the chloride concentration may be increased such that the plugs of the second perforation tool 904 are dissolved after the fracturing of the formation 916 has been completed.

While embodiments with one or two perforation tools have been described herein, more than two perforation tools may also be used to perform variants of the methods described herein. For example, a well could have as many or more than 25 perforation tools to realize a desired completion and production regime.

Use for Production

It will be appreciated that the perforation tools and methods described herein may be equally advantageous for production apart from the benefits derived in well completion, including fracturing. For example, a perforation tool described herein may be used to control the time after which production from certain production zones may begin. Advantages of production-related uses include that there would be no need to perforate the casing to start production as holes would be created after the dissolvable plugs eventually dissolve. As described above, such dissolution may occur automatically or after fluid properties in the well fluid are manipulated. 

1. A perforation tool for use in a production well, the perforation tool comprising: a tubular housing having a wall defining a channel, the housing comprising one or more holes, each hole extending through the wall; and one or more dissolvable plugs, each dissolvable plug connected to the housing in order to seal the respective hole, wherein each dissolvable plug comprises dissolvable material that extends from an interior face of the housing to an exterior face of the housing such that when the dissolvable material is dissolved, fluid communication through the wall is enabled via the holes.
 2. The perforation tool according to claim 1, wherein each dissolvable plug and respective hole are connected by complementary screw threads.
 3. The perforation tool according to claim 1, wherein the dissolvable material comprises magnesium.
 4. The perforation tool according to claim 1, wherein the housing comprises between about 5 and about 50 holes.
 5. The perforation tool according to claim 1, wherein each hole has a cross section at the interior face of the housing of between about % and about % inch.
 6. The perforation tool according to claim 1, wherein the holes are arranged in a longitudinal spiral about the housing, each hole being radially disposed between 30° and 90° from a neighboring hole in the longitudinal spiral.
 7. The perforation tool according to claim 1, wherein the housing further comprises: a first section with a box thread to connect the housing to a first section of production casing; and a second section with a pin thread to connect the housing to a second section of production casing.
 8. A method for fracturing a production zone, the method comprising the steps of: providing a perforation tool according to claim 1 in a well proximal to the production zone; dissolving one or more of the one or more dissolvable plugs; and providing fluid to the production zone through holes with a dissolved plug to fracture the production zone.
 9. The method according to claim 8, wherein the dissolving step is performed at between about 2,000 and about 10,000 psi.
 10. The method according to claim 8, wherein the dissolving step is substantially completed within about 3-7 days.
 11. The method according to claim 8, wherein the tubular housing forms part of the production casing.
 12. The method according to claim 8, wherein the dissolving step is performed at between about 10 wt % and about 25 wt % chlorides.
 13. The method according to claim 8, wherein the dissolving step is performed at between about 0 wt % and about 10 wt % chlorides.
 14. The method according to claim 8, wherein the dissolving step comprises providing an acid to the dissolvable plugs.
 15. The method according to claim 8, further comprising the steps of: providing a second perforation tool according to claim 1 in the well proximal to a second production zone; dissolving one or more of the one or more dissolvable plugs of the second perforation tool; and providing fluid to the second production zone through holes of the second perforation tool with a dissolved plug to fracture the second production zone.
 16. The method according to claim 15, further comprising the step of providing a diverter to the first perforation tool to prevent fluid flow to the first production zone.
 17. The method according to claim 16, wherein the providing the diverter step is performed simultaneously with the providing fluid to the first production zone.
 18. The method according to any claim 15, wherein the dissolvable plugs of the second perforation tool dissolve at a slower rate than the dissolvable plugs of the first perforation tool.
 19. The method according to claim 15, wherein the first production zone and the second production zone belong to a same formation.
 20. The method according to claim 15, wherein the step of dissolving one or more of the plurality of dissolvable plugs of the first perforation tool comprises providing a first dissolving fluid to the first perforation tool, and the step of dissolving one or more of the plurality of dissolvable plugs of the second perforation tool comprises providing a second dissolving fluid to the second perforation tool. 